What is a Logic Level Power MOSFET ?

Power MOSFET transistors are voltage controlled switches.  They begin to turn on at their rated “gate threshold voltage” or Vgs(th).  Most of the datasheet ratings are given for a fully saturated condition, typically 10 volts.  There is also a maximum allowable gate voltage, Vgs, that is typically 20 volts.  Any voltage greater than that will pierce the thin metal oxide layer that insulates the gate from the rest of the silicon die, destroying the device.  This is why uninstalled MOSFETS can be so sensitive to electrostatic discharge (ESD) damage.  

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The Democrats Balanced Plan for the Federal Budget

The democrats and President Obama say they want a balanced approach to the Federal Budget crisis. 

They propose equal parts of:

• Tax more
• Spend more
• Borrow more

See?  Balanced!

Microchip PIC Microcontrollers for Motor Control: PIC16F648, PIC16F785 and PIC18F2331

While many of the PIC microcontroller models have at least one hardware PWM output channel that could be used to control an h-bridge, we’ll take a quick look at several models that are particularly well suited for servo and stepper motor control applications.  

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Allegro A3977 Microstepping Stepper Motor Control IC Review

Configuration: Dual H-Bridge w/ microstepping translator
Applications: Stepper Motor
Current (peak): 2.5 amps
Voltage (max): 35V
Short circuit protection: No
Built-in chopper current limitation: Yes, Full and half stepping, 4 and 8 microsteps
Interface: Step and Direction

A3977 PCB

With dual h-bridges and a built-in translator, DAC and chopper circuits, the A3977 is a nearly complete microstepping stepper motor controller on a single chip.  With the addition of a handful of external passive components, this IC is ready to accept step & direction signals from a pulse generator, microcontroller, indexer or CNC controller.  Each pulse applied to the Step input rotates the motor one microstep forward or reverse, depending on the state of the Direction input. 

National Semiconductor LMD18245 Motor control IC Review

Configuration: Single H-Bridge
Applications: PM DC, Servo, Stepper
Current (continuous): 3 amps
Current (peak): 6 amps
Voltage (max): 60V
Short circuit protection: Yes
Built-in chopper current limitation: Yes, 4-bit linear DAC
Interface: Parallel
Datasheet: LMD18245

Thanks to its voltage and current capability, the LMD18245 is suitable for driving small PMDC servo motors or a medium size stepper motor winding.  It incorporates a unique lossless current sense output.  This chip also includes a 4-bit linear DAC to generate a reference voltage for the internal chopper circuit.  When used in pairs, these chips can run a stepper motor at up to 8 microsteps per full step with reasonable accuracy.   The LMD18200 is a similar IC that lacks the DAC and chopper circuit. 

National Semiconductor LMD18200 Motor control IC Review

Configuration: Single H-Bridge
Applications: PM DC, Servo, Stepper
Current (continuous): 3 amps
Current (peak): 6 amps
Voltage (max): 60V
Short circuit protection: Yes
Built-in chopper current limitation: No
Interface: Parallel
Datasheet: LMD18200

Thanks to its voltage and current capability, the LMD18200 is suitable for driving small PMDC sevo motors or a medium size stepper motor winding.  It incorporates a unique lossless current sense output that can be used by an external circuit for chopper current control.  The LMD18245 is a very similar part that adds a 4-bit linear DAC and built-in chopper circuit.

Infineon TLE6209R Motor control IC Review

Configuration: Single H-Bridge
Applications: PM DC, Servo
Current (continuous): 6 amps
Current (peak): 7 amps
Voltage (max): 40V
Short circuit protection: Yes
Built-in chopper current limitation: 4, 5, 6 or 7 amps
Interface: Parallel & SPI serial for settings
Datasheet: TLE6209R

The TLE6209R has in interesting combination of parallel inputs for direct control of the h-bridge with a serial SPI interface for the internal settings such as current limit and chopper off time.    Along with shout circuit protection, the chip has a selectable current limit.  This might be used to limit motor current during startup, providing something like a soft-start function.

Infineon TLE5205 and TLE5206 Motor control IC Review

Configuration: Single H-Bridge
Applications: PM DC
Current (continuous): 5 amps
Current (peak): 6 amps
Voltage (max): 40V
Short circuit protection: Yes
Built-in chopper current limitation: No
Control Interface: Parallel
Datasheet: TLE5205 TLE5206

The TLE5205/6 is a simple and robust looking driver chip with only 7 pins and minimal external components required.  The main drawback is that the drivers have a rather long turn-on delay and switching time (in the tens of microseconds.)  This makes it unsuitable for chopper current regulation and PWM operation at typical frequencies.  However, it should work well for on-off control in applications such as electric car windows or linear actuators. 

The only difference between the TLE5205 and TEL5206 is the control logic truth table.  The 5206 maps each of the two input pins directly to one of the output pins.  Each half-bridge output is either sourcing of sinking depending on the high or low state of its corresponding input pin.  This permits only forward, reverse and dynamic braking.  The 5205, on the other hand, has a different truth table that allows for the addition of an all-outputs-off coast mode.

Stupid Warning Labels, But Not The Kind You Think

We’ve all seen the caution us not to do idiotic things or remind us of the obvious.  “Remove infant before folding stroller” and “Do not use toaster while bathing” are two examples that come to mind at random.  But what about warning labels that really do need to convey important, non-obvious information?  They can be stupid too. 

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How to Convert USB to Serial TTL Level Signals

If you’re designing a device that spends most or all of it’s time connected to a PC through a USB port, it is probably best to design USB connectivity right into the device.  However, if the device only needs to be connected occasionally to change settings or download data logs, it might be convenient to use a separate adapter that translates USB protocol to TTL level asynchronus serial signals that talk to the microcontroller’s UART.  Also, if you’re a hobbyist, you may not want to spend a lot of time understanding the details of USB interfacing hardware and protocols.  I recently stumbled upon an adapter that makes this easy.   

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